The overall objective of this research proposal is to investigate the substrate uptake systems and intermediary metabolism of isolated retinal microvessels in order to determine the effects of hyperglycemia on these processes and to elucidate their possible control by insulin-receptor mediated interactions. The isolation of purified preparations of bovine retinal microvessels in our laboratory and the demonstration that these tissue preparations are metabolically active and responsive to the effects of insulin, have provided a unique experimental system to study the response of the isolated microvasculature of the retina to metabolic and hormonal influences which may be central to the pathogenesis of diabetic retinopathy. Although the metabolic consequences of insulin lack or resistance, and its accompanying hyperglycemia appear primary to the microvascular complications of diabetes the specific effects of this hormone on microvascular metabolism have only now begun to be investigated. Since the uptake and metabolism of glucose and fructose, the two principal dietary carbohydrates, may be altered in the microvascular and neural tissue of the retina in diabetes, an understanding of these processes and their control is essential to the elucidation of the metabolic basis for the microvascular pathology of diabetes in this tissue. The proposed experiments will examine the hypothesis that in diabetes-induced hyperglycemia excessive lactic acid is produced in the retina and its microvasculature as a result of increased metabolism of glucose and fructose via the pathway of anaerobic glycolysis, and because of possible reduced utilization of glucose and fructose for glycogen synthesis and pyruvate for oxidative metabolism due to the loss of insulin control of the key enzymes in the latter pathways, glycogen synthetase and pyruvate dehydrogenase respectively. The specialized metabolism of glucose to fructose via the sorbitol pathway will also be examined as a possible alternate and pathogenic route of metabolism of these sugars. This research should shed light on the reported differential metabolism of glucose and fructose by the retina and the extent of their conversion to sorbitol and lactate, potentially toxic metabolites which may play a role in the pathogenesis of diabetic retinopathy.